The present invention is related to a high-density granular detergent composition and a product made therefrom, and to a dry neutralization process for preparing the granular detergent composition.
There has recently been considerable interest in the detergent field in high-density detergent powders having a high surfactant active level. These concentrated products can be packaged in smaller containers to provide savings in manufacturing and shipping over conventional spray-dried products, and their compact size is appreciated by consumers.
Numerous methods of making high density, high active granular detergent products have been suggested in the past, including dry neutralization processes. European Patent Publication 0,352,135 (Unilever) discloses a process comprising the steps of neutralizing a detergent acid (eg, linear alkylbenzene sulfonic acid) with a particulate water-soluble alkaline inorganic material (eg, carbonate) in equipment which provides both a stirring and a cutting action (eg, a Fugae or a Lodige), while maintaining the temperature of the product at 55.degree. C. or less. Also disclosed is the addition of powdered surfactant to the process prior to the addition of the sulfonic acid.
Great Britain Patent Publication No. 1,369,269 (Colgate-Palmolive Company) discloses a process for dry neutralizing a synthetic organic anionic detergent acid with a particulate neutralizing agent, for example, carbonate, under high shear mixing conditions. The product made is finally divided and free-flowing, and may be blended directly with other detergent materials, or further reduced in particle size as necessary to suit the final product requirements.
A slightly different process for preparing high-density detergent products is disclosed in JP 60-072999A (Kao) wherein detergent sulfonic acid, sodium carbonate and water are mixed in a high-shearing apparatus to produce a solid mass which is further pulverized into a fine powder and then granulated into the desired high-density detergent product.
Alkyl sulfate surfactant is a valuable anionic surfactant in detergent products, particularly when used in combination with another anionic detergent surfactant such as alkylbenzene sulfonate surfactant. Processing of alkyl sulfate surfactants into detergent products can sometimes be problemsome when the alkyl sulfate is exposed to acidic conditions, since the alkyl sulfate surfactant can undergo unwanted hydrolysis to fatty alcohol.
Various methods of incorporating alkyl sulfate surfactant into high density, high active detergent products have been suggested, none of which are completely satisfactory. For example, the above mentioned Kao Publication JP 60-072999A discloses the incorporation with the detergent acid of the alkyl sulfate in liquid form. The mixing of the alkyl sulfate with the acid complicates the handling of the material, and will result in some appreciable level of reversion of the alkyl sulfate to the corresponding fatty alcohol by acid-catalyzed hydrolysis. Commonly assigned U.S. patent application Ser. No. 364,721, filed Jun. 9, 1989 (Muellar et al), now U.S. Pat. No. 5,152,932, discloses a process for producing high active detergent particles comprising the steps of continuously reacting alkyl sulfonic acid and/or alkylbenzene sulfonic acid with concentrated alkali metal hydroxide solution to produce a neutralized product with less than about 12% water, adding thereto a polyethylene glycol or ethoxylated nonionic surfactant, and forming detergent particles therefrom.
The alpha-sulfonated fatty acid alkyl ester surfactant is also useful as a detergent surfactant. This surfactant is attractive since it can be prepared partly or wholly from natural, renewable, non-petrochemical feedstocks and since it has good cleaning power without being sensitive to calcium ion in wash solutions. Alpha-sulfonated fatty acid alkyl ester can be used with other detergent surfactants, including anionic surfactants such as alkylbenzene sulfonate and alkyl sulfate surfactants. It is known that alpha-sulfonated fatty acid alkyl ester salts are susceptible to hydrolysis during their production, processing, and storage. Under alkaline conditions greater than about pH 10, the ester can undergo irreversible hydrolysis to the disalt of alpha-sulfo fatty acid, and the corresponding fatty alcohol. Under acidic conditions (less than about pH 6) as well, and in the presence of moisture, the ester can undergo reversible hydrolysis to the disalt and fatty alcohol. The disalt is weakly soluble in water and possesses only poor washing and cleansing power. Conventional methods of incorporating alpha-sulfonated fatty acid alkyl ester into heavy duty granular detergent products are not completely successful. As described in U.S. Pat. No. 4,416,809 (Magari et al, Nov. 22, 1983), the slurrying and spray drying at high temperature of compositions containing alpha-sulfonated fatty acid ester in the presence of strong alkaline builder, including sodium silicate and sodium carbonate, can result in hydrolysis of the ester and high levels of the undesirable disalt in the product.
Another useful detergent surfactant is polyhydroxy fatty acid amide. This surfactant is also attractive as derivable from natural, renewable, non-petrochemical sources. Examples of such polyhydroxy fatty acid amides are described in copending U.S. patent application Ser. No. 07/589,740 filed Sep. 28, 1990, now U.S. Pat. No. 5,494,982, incorporated herein by reference. The polyhydroxy fatty acid amide surfactant can be used in a granular detergent product along with other detergent surfactants, particularly anionic surfactants such as alkylbenzene sulfonate and alkyl sulfate surfactants. It is known that amides, much like esters, undergo hydrolysis in both acidic and alkaline conditions. Under alkaline conditions of greater than about pH 11, and under acidic conditions of less than about pH 3 and in the presence of moisture, the amide can be hydrolized irreversibly to the corresponding amine and fatty carboxylate salt (or fatty acid). These hydrolysis products are not as useful for cleaning as the amide surfactant, and are in fact highly undesirable in the final product. Since a very low level of amine can produce malodor in the product, hydrolysis of the polyhydroxy fatty acid amide should be completely avoided.
As used hereinafter, the term "pH sensitive detergent surfactant" refers to alkyl sulfate, alpha-sulfonate fatty acid alkyl ester, and polyhydroxy fatty acid amide, and mixtures thereof. The surfactant can undergo undesirable hydrolysis under acidic pH conditions, particular at a pH of less than about 6 and in the presence of moisture, and under alkaline pH conditions, particularly above about pH 9.